Electric power distribution assembly employing a joint compound



Aug. 30, 1966 H. G. PFEIFFER ELECTRIC POWER DISTRIBUTION ASSEMBLY EMPLOYING A JOINT COMPOUND Filed April 27, 1964 a! e -.nT M I? n w i I- n o r/oalhfl e6 6 vz h m W [W 6 E F v N L b 6 la d 1; Mo r M Z S 2 0 1 p, I; 0 i w m C L 0 m m m m m m z w United States Patent 3,270,121 ELECTRIC POWER DISTRIBUTION ASSEMBLY EMPLOYING A JOINT COMPOUND Heinz G. Pfeilfer, Schenectady, N.Y., assignor to General Electric Company, a corporation of New York Filed Apr. 27, 1964, Ser. No. 362,804 Claims. (Cl. 174--88) This invention relates to stabilizing the connections between'power transmitting conductors such as are commonly encountered in busway joints by treatment of the mutual contact surfaces and more particularly to joint compounds for providing such stabilization thereby insuring long term low electrical resistance values at the joints between such conductors.

In electrical power distribution assemblies the resistance of joints in flat bus bars either singly or in busway systems depends on the accumulative efiect of several factors; the amount of overlap of the bars, the contact pressure therebetween and the effectiveness of the preparation of the contact surfaces. The larger the overlap, the smaller the resistance increase at the joint. In practice, overlaps of bus bars of from about to about times the cross-sectional area of the bar are employed.

One common method of joint preparation for bus bar surfaces at the joint, particularly with bus bars made of aluminum, alone or in the form of an aluminum alloy, or copper, has been to abrade the surfaces with emery cloth, Wipe the surfaces clean, smear Vaseline over the surfaces, rub the Vaseline lightly against the surfaces with fine emery cloth and then effect the juncture without wiping the Vaseline from the surfaces. The resistance of joints in the case of aluminum bus bars shortly after preparation in this manner may be very low, however, after extended periods of operation the joint resistance rises objectionably. As used in this specification aluminum and aluminum metal composition include both pure aluminum and alloys of aluminum containing at least 50% aluminum.

In order to maintain the joint resistance below on an acceptable level, the only reliable surface treatment for bus bars of aluminum metal composition has been the application of a thin coating of silver over each contact surface. Although this treatment is relatively successful in providing long term low joint resistance, the expenditure entailed is considerable. Therefore, manufacturers of switch gear for electric power control have been particularly desirous of developing substitute means for effecting busbar joint treatment to avoid the high cost of the silver coating and its application and yet retain the value of joint resistance below an acceptable level.

It is therefore a primary object of this invention to provide an economical and reliable material for the treatment of the contact surfaces of the joints of electrical power conductors to obviate the commonly occurring increase of joint resistance with consequent decrease in the power transporting capabilities of the electrical power conductors.

It is a further object of this invention to provide a method for the stabilization of the electrical characteristics of joints of bus bars of aluminum metal composition subject to temperature cycling to secure long term low joint electrical resistance at a relatively low cost.

It is still another object of this invention to select a class of joint compounds having the unique capacity of being able to alter the electrical characteristics over the surface of aluminum conductors where applied to maintain the value of the electrical resistance between contacting surfaces of aluminum bus bars so treated below some long term accepted maximum value.

It has been found that the above objects inure in particular to aluminum bus bar joints the contact surfaces of which have been treated with a joint compound selected from the class of monoolefinic compounds containing a polar group and a long chain saturated aliphatic group.

The exact nature of this invention as well as other objects and advantages thereof will be readily apparent from consideration of the following specification relating to the annexed drawing in which:

FIG. 1 is a three dimensional View illustrating an opened joint in a typical busway construction in which this invention may be employed;

FIGS. 2 and 3 schematically illustrate the overlapping relationship of individual bus bars in the busway construction of FIG. 1 before and after connection; and

FIG. 4 is a graph displaying the relative performances with respect to electrical resistance of bus bar joints prepared in different manners as a function of temperature cycling.

In order to determine the stabilizing effect afforded for the joints of bus bar construction by treatment of the conductor contact surfaces with joint compounds according to this invention, the joint construction of a busway system shown in FIG. 1, and more completely described in US. 3,124,642, was employed in order to provide a basis for comparison with previously known techniques of joint preparation. The conduction of electricity between b-usway sections 11 and 12 takes place through the contact, or overlap, area between mating bus bars 13 and 14.

To duplicate actual operating conditions as closely as possible, joints prepared with the particular treatment under test were subjected to extensive temperature cycling and the resistance of the test joints Were in each instance measured at the end of established cycling periods by means of a Kelvin double bridge employing a constant probe distance across each joint. During the tests a current load of 150 amperes was applied to the assembly thereby causing a temperature rise in the joints. A control thermocouple (not shown) was employed to control the power supply so that a temperature of C. was held during the ON portion of the cycle. The cycle was 15 minutes ON and 45 minutes OFF. During the OFF portion of the cycle the joint'was allowed to cool to room temperature (about 25 C.). In raising the busway to the control temperature (100 C.) by the resistance heating of the current flow, a period of about 12 minutes was required during each cycle.

When the connection between sections 10 and 1.1 is completed, bus bars 13 and 1 4 are urged into closed contact by springs 16 as shown in FIGS. 2 and 3 to improve current transmission. This type of construction enables greater relative displacement between bus bars 1.3 and '14 during the temperature cycling and reflects a more severe operating condition than would be encountered in a bolted bus bar joint construction.

The novel joint compounds for stabilizing the resistance of power conductor joints in accordance with invention are monomeric compounds having the general formula where n is one of the integers 0, 1, R is a monovalent radical selected from the group consisting of hydrogen and fluorine, R is a monovalent radical selected from the group consisting of hydrogen, fluorine, methyl, monofiuoromethyl, difluoromethyl, and trifluoromethyl, X is a divalent radical selected from the group consisting of is the representative of the following more specific tormulae:

When n is 0, it represents the two radicals and when n is 1, it is representative of the following three formulae:

R- C=( JCRz- R R R( 3=( JORz- R R R It will be recognized that when R is either hydrogen or fluorine, Formulae (a) and (b) represent the same radicals, and Formulae (c), (d) and (e) also represent the same radicals. However, when R is methyl, or one of the three fiuoromethyl radicals, all four formulae represent different radicals.

Typical of the radicals represented by Formulae (a) and (b) are, for example, vinyl, propenyl, l-methylvinyl and the [fluorine-substituted derivatives of these three hydrocarbon radicals, for example, l-fluorovinyl, 2 fluorovinyl, 1,2-difluorovinyl, 2,2-difluorovinyl, 1,2,2-trifluorovinyl, l-tfluoropropenyl, Z-fiuoropropenyl, 3,3-difluoropropenyl, l-(dluoromethyDvinyl, l-methyl-Z-fluorovinyl, 1-(trifiuoromethyDvinyl, 1-triflu0romethyl-2,2 difluorovinyl, etc.

Typical of the radicals covered by Formulae (c), (d) and (e) are, for example, allyl, crotonyl, (Z-butenyl), isocrotonyl, (2-isobutenyl), l-methylallyl, Z-methylallyl and the fluorinesubstituted derivatives of these live bydrocarbon radicals, for example, 1-filuoroallyl, -2afluoroallyl, 2,3-di fluoroallyl, 2-dluoroisocrotonyl, 4,4-difiuorocrotonyl, l-methyl-3- flu0roallyl, 2-(fluoromethyl)allyl, 2-( fluoromethyl)-3-fiuoroallyl, 1-(trifiuoromethyl)a1lyl, 2- trifluoromethyl -3 ,3 -difluoro allyl, etc.

Typical examples of radicals represented by R" are the linear alkyl radicals, e.*g., undecyl, dodecyl, tridecyl, tetradecyl, hexadecyl, octadecyl, nonadecyl, eicosyl, docosyl, tricosyl, heptacosyl, tr-iacontyl, dotriacontyl, tetracontyl,

pentacontyl, hexacontyl, and the .fiuorosubstituted derivatives of these hydrocarbons, in which one or more, up to all, of the hydrogen atoms have been substituted by a fluorine atom. Typical of the linear fluoroalkyl radicals are, by way of example, the mono-, di-, tri-, tetra-, penta-, hexa-, up to pentacosylfiuorododecyl, the mono-, di-, tri-, tetra-, penta-, etc., up to hentetracontylfiuoroeicosyl, etc., radicals.

The compounds are monoolefinic alkyl ethers when X is oxygen; monoolefinic alkyl ketones when X is carbonyl; monoolefinic alkyl carbonates when X is carbonate; and may be either the monoolefinic alcohol ester of an alkyl carboxylic acid, or an alkyl alcohol ester of a monoolefinic unsaturated carboxylic acid when X is carbonyloxy.

Typical examples of the various compounds falling within this general formula are as follows:

Vinyl undecyl ether, vinyl undecyl ketone, vinyl undecyl carbonate, undecyl acrylate, vinyl laurate, vinyl tetradecyl ether, vinyl hexadecyl ether, vinyl octadecyl ether, vinyl eicosyl ether, vinyl tricosyl ether, vinyl triacontyl ether, vinyl pentacontyl ether, vinyl hexacontyl ether, l-methylvinyl dodecyl ether, Z-methylallyl dodecyl ether, crotenyl dodecyl ether, crotonyl hexadecyl carbonate, hexadecyl acrylate, dodecyl methacrylate, octadecyl vinylacetate, eicosyl crotonate, tricontyl tiglate, vinyl stearate, vinyl palmitate, allyl stearate, crotonyl behanate, vinyl myristate, dodecyl vinylacetate, l-methylallyl docosyl ketone, crotonyl nonadecyl carbonate, etc., including the fluorine substituted derivatives of these compounds wherein one or more hydrogen atoms are substituted for the fluorine atom, for example, fiuorovinyl dodecyl ether, fluorocrotonyl tricosyl carbonate, 2-fiuoromethylallyl eicosyl ketone, hexadecyl trifluoroacrylate, tetradecyl fluoromethacrylate, 2-fiuoroallyl myristate, etc.

Because of the ready availability of raw mataerials and ease of synthesis, and the suitability and outstanding properties as joint compounds, we prefer to use the vinyl, allyl and crotonyl esters of the saturated fatty acids (linear alkyl carboxylic acids) having from 11 to 24 carbon atoms in the alkyl groups of the carboxylic acid, or crotonic acid esters of linear alkyl alcohols having from 11 to 24 carbon atoms.

All of the above materials may be used alone, mixed with each other, or mixed with viscosity modifiers, for example, mineral oils, greases, silicone oils, diester oils, etc.

Although a complete theoretical explanation is as yet unavailable for this unexpected performance it may at least be stated that the surface active properties of these monomeric compounds, not only improve the initial electrical contact between metallic conductors, particularly aluminum, but the use of these joint compounds actually stabilizes the electrical behavior of the joint so that improved electrical contact is maintained over extended periods of time.

Experiment has shown that when applied to a pair of aluminum surfaces to be placed into mutual contact, monoolefinic compounds in the unpolymerized (monomeric) state will become attached to the surface of the metal at the locus of the unsaturated bond of the compound and cling tenaciously to the surface providing therefore excellent protection from oxidation. What connection this behavior has to the ability of these compounds to stabilize the electrical behavior of such a joint has not been definitely established but it has been determined that the action occurring between the aforementioned unsaturated bond and the surface of the aluminum is necessary. Based upon this action between compound and metal in view of the specific exam les disclosed herein using vinyl stearate, a-olefins alone and in combination with polar compounds as set forth herein are useful as stabilizers for joint electrical resistance.

Comparative and absolute beneficial performance of the joint compound of this invention is displayed in Table I and forms in part the basis for the graphic representation in FIG. 4:

TABLE I A. Silver plated aluminum conductors Cycles 1 I 2 l 3 4 y 5 I 6 TABLE II B. Monomeric compound-coated aluminum conductors Cycles 7 8 9 10 11 12 Curve 20 in FIG. 4 displays the average performance of the silver plated aluminum conductors described in Tests 1-6. It is evident that for a relatively extended period of use the value of the joint resistance remains appreciably below the maximum design value for the set of test conductors represented by line 22. Since the contact area of the test conductors was about 0.375 sq. in., the maximum allowable design value amounted to a resistance of about 1600 ohms/sq. in.

Graph 21 similarly represents the performance of bare aluminum conductors coated with monomeric compound in Tests 7-12. It may be seen that the joint resistance values obtained actually reflect improved performance over the use of silver plated aluminum conductors, the commonly employed expedient and these values remain well below line 22 for an indefinite time.

Dotted line curve 23 has been included to show the drastic rise in joint electrical resistance, which occurs in aluminum bus bar joints employing untreated commercially prepared bare aluminum conductor surfaces. Tests have shown that in tightly bolted untreated bare aluminum-to-aluminum bus bar connections exposed to temperature cycling involving a temperature change of only about 55 C. (the usual maximum design temperature rise) the value of the joint resistance increases at an extremely rapid rate after as little as 300 hours of exposure. The metal surface smoothness of both the aluminum conductors in this test and also in the Tests 7-12 was unaltered from the regular finish produced during normal commercial preparation of electrical conductors.

With respect to the monomeric compound preparations employed to coat the aluminum conductors for Tests 7, 8 and 9 (above) were coated with the following composition:

- Grams Vinyl stearate 400 Dioctyl azelate 400 Lithium hydroxy stearate 240 Hydroquinone 2.6 Phenyl a naphthyl amine 2.6

Grams Vinyl stearate 340 Dioctyl azelate 60 Lithium hydroxy stearate 60 6 The latter composition has the consistency of a heavy grease.

The silver plating for the silver plated aluminum conductors was prepared by applying first a zinc coating and then electroplating silver over the bus bar to a thickness of 0.0002 inch.

Preparation of the aluminum contact surfaces of bus bar joint 10 may be eifected by various methods each of which serves the prime purpose of applying a coating of the monomeric compounds over the bare metal surface prepared according to regular commercial practices, that is, without unusual surfacing operations to provide exceptionally flat, smooth contact faces. For example, one method, which has been employed is to abrade the contact areas with emery paper while these contact areas are covered with a 30/70 vinyl stearate/ kerosene solution. The wet abrasion process is repeated three or four times and finally the contact areas are each wetted once more with the solution and the conductors are placed in surface contact.

Although one method of applying the joint compounds of this invention to the surface of the bare aluminum conductors has been described above, any sequence of operations which encourages intimate contact between the monomeric joint compound and the bare surface of the aluminum will provide an operative disposition over the contact surfaces. Thus, on a freshly cleaned surface of aluminum, it is merely necessary to lightly rub the olefinic joint compounds of this invention thereover.

Various modifications, as for example, in the particular mode of application of the joint composition to the bus bar surfaces, specific busway construction including various means of biasing the bus bars into close electrical contact are contemplated and may be obviously resorted to by those skilled in the art without departing from the spirit and scope of the invention as hereinafter defined by the appended claims as only an exemplary embodiment has been disclosed.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electrical power distribution assembly comprising:

(a) a plurality of electrical power bus bars,

(1) said bus bars being disposed relative to each other with portions of the ends thereof in overlapping relationship,

(b) a layer of a joint compound disposed between said bus bars in each area of overlap stabilizing the resistance in each area of overlap at a value below about 1600 ohms/sq. in.,

(1) said joint compound comprising a substantial pound containing a divalent radical selected quantity of :a mixture of an a-olefin and a compound containing a divalent radical selected from the group consisting of and carbonyloxy (C0) tial quantity of a monoethylenically unsaturated compound having the formula carbonyloxy (-("JO) and R" is a monovalent radical selected from the group consisting of linear alkyl radicals having at least 11 carbon atoms and linear fluoroalkyls having at least 11 carbon atoms, and

(c) means for continuously biasing said overlapping ends into effective electrical contact.

3. The electrical power distribution assembly construction recited in claim 2 wherein the monoethylenically unsaturated compound is vinyl stearate.

4. In an electrical power distribution assembly wherein a plurality of electrical conductors are disposed relative to each other with portions thereof arranged in overlapping relationship and urged into effective mutual electrical contact, the improvement consisting of a coating of a joint compound disposed between said overlapping portions, said joint compound comprising a substantial quantity of a material selected from the group consisting of:

(a) a mixture of an a-olefin and a compound containing a divalent radical selected from the group consisting of if and carbonyloxy (CO) and (b) a monoethylenically unsaturated compound having the formula B (R) CR=C-(CR)nXB/ carbonyloxy ((iO-) and R" is a monovalent radical selected from the group consisting of linear alkyl radicals having at least 11 carbon atoms and linear fluoroalkyls having at least 11 carbon atoms. 5. The improvement recited in claim 4 wherein the joint compound is vinyl stearate.

References Cited by the Examiner UNITED STATES PATENTS 2,906,987 9/1958 FOX.

LEWIS H. MYERS, Primary Examiner.

DARRELL L. CLAY, Examiner. 

1. AN ELECTRICAL POWER DISTRIBUTION ASSEMBLY COMPRISING: (A) A PLURALITY OF ELECTRICAL POWER BUS BARS, (1) SAID BUS BARS BEING DISPOSED RELATIVE TO EACH OTHER WITH PORTIONS OF THE ENDS THEREOF IN OVERLAPPING RELATIONSHIP, (B) A LAYER OF A JOINT COMPOUND DISPOSED BETWEEN SAID BUS BARS IN EACH AREA OF OVERLAP STABILIZING THE RESISTANCE IN EACH AREA OF OVERLAP AT A VALUE BELOW ABOUT 1600 OHMS/SQ. IN., (1) SAID JOINT COMPOUND COMPRISING A SUBSTANTIAL QUANTITY OF A MIXTURE OF AN A-OLEFIN AND A COMPOUND CONTAINING A DIVALENT RADICAL SELECTED FROM THE GROUP CONSISTING OF 